在controller類中

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(String.class, new StringFormat());
}

    class StringFormat extends PropertyEditorSupport{
            //text時前端傳的引數值
            //setValue設定引數傳到後臺時的值
        @Override
        public void setAsText(String text) throws IllegalArgumentException {
            if
 
(text == ""){
                setValue("為空");
            }else{
                setValue(text); 
            }
        }
    }